Marginal Cases Versus Species Normality

There is no morally relevant property uniquely possessed by all humans that means all and only humans deserve direct moral consideration. This is known as Singer's Argument from Marginal Cases. It poses the challenge of coming up with this morally relevant property. It cannot be the ability to talk because some humans, so-called `marginal cases,' are born without this ability, yet most believe marginal cases still deserve direct moral consideration. In this essay I consider the Argument from Species
Normality as a counterargument to the Argument from Marginal Cases. This is the argument that marginal cases deserve direct moral consideration, while animals do not, because marginal cases belong to a species that usually does possess the morally relevant property. I argue that the Argument from Species Normality is a weak counterargument as it rests on a morally arbitrary distinction between species.